In all honesty, there will be no way to define your relationship with your family member until you actually visit and assess it in person. With mental illness it is an ever changing canvas even if some symptoms persist. If the rest of the family as you said haven’t done their homework so to speak that makes it a bit more challenging (in my opinion) I would gently try to enlighten your family that is the caregivers to NAMI and their resources and free classes and maybe let them know about the book by Xavier Amador entitled “I’m Not Sick, I Don’t Need Help”. The care giving part of your family may not want help or advice either-or maybe they will.
Aside from that I would try to approach your sibling without any preconceived ideas or expectations. Just a meet and greet to start and then see what he or she feels comfortable with. It could be just a walk or watching a favorite TV show or sharing a simple meal. Even good things like gifts and helping and cleaning etc… can be stressful for the ill person, (my sister is like that)
I would ask if she or he wants the help and try to go with what they say unless it affects health or safety.
Stress makes symptoms worse. Unfortunately it is sometimes hard to see what the ill person’s stressors are until they happen. Often what stresses them out would not phase us at all, their brain is operating so differently than ours. If it were me I would consider my first visit a kind of subtle fact finding mission of sorts, no expectations, just a friendly visit…quiet and understated, maybe one small useful gift, a favorite food or drink maybe,or a favorite dvd or CD if that applies.
Conversationally I would try to keep questions at a minimum and try to just “be” with your sibling and quietly observe how they react and respond to their environment and you being there, where their focus is or isn’t and their body language. Maybe follow their lead if they come up with a good way to spend your time together.
That is my best advice, then on future visits you can make changes as needed or do the same thing again just to get a better overview of set behaviors and ones that seem to change often…anyway, good luck with your visits, I hope it all goes really well.